Abstract LB235: Mechanistic studies on VNLG-152R-mediated tumor inhibition of triple negative breast cancer
Authors: Elizabeth Thomas, Retheesh S. Thankan, Puranik Purushottamachar, Vincent C. Njar
Journal: Cancer Research (2023)

Abstract Introduction: Breast cancer remains a major concern as the second leading cause of cancer-related death in women in the United States and the most frequently diagnosed cancer in women globally. Among all the subtypes, triple negative breast cancer (TNBC) is highly resilient and eludes currently available treatment modalities. This study describes the mechanism of action of VNLG-152R in inhibiting TNBC tumor growth. Methods: TNBC cell lines MDA-MB-231 and MDA-MB-468 originated from TNBC patients of Caucasian American and African American descend, respectively, were challenged with VNLG-152R in vitro. The mechanism of action was studied by immunoblotting key proteins, proteasomal degradation assay of Mnk1/2 and transcriptome analysis by RNA-seq. The therapeutic potential of VNLG-152R is demonstrated in NRG mice bearing either MDA-MB-231 or MDA-MB-468 tumor xenografts. Results: We report for the first time, that, VNLG-152R significantly upregulates Synoviolin (SYVN1) in TNBC cell lines MDA-MB-231 and MDA-MB-468 with concomitant degradation of Mnk1/2. SYVN1 is a known E3-ubiquitin ligase and it ubiquitinates its target proteins, rendering them to proteasomal degradation. However, there was no significant change in Mnk1/2 levels upon treatment with VNLG-152R in presence of SYVN1 inhibitor LS102. A similar result is obtained upon siRNA knockdown of SYVN1. Subsequently, the decreased level of Mnk1/2 diminished the phosphorylation of eIF4E with a concurrent decrease in levels of eIF4E-validated downstream targets, Bcl-2 and Cyclin D1, resulting in tumor growth inhibition. Inhibition of proteasomal degradation by MG-132 prior to treating cells with VNLG-152R further supports that VNLG-152R promotes SYVN1-mediated ubiquitin-proteasomal degradation of Mnk1/2. Further, RNA-seq and Gene Set Enrichment Analysis (GSEA) of differentially expressed genes demonstrate inhibition of mTORC1 (mammalian target of rapamycin complex 1) and NUP153 (Nucleoporin 153) pathways and activation of p53 pathway thereby inhibiting tumor progression. Finally, oral administration of VNLG-152R to mice bearing tumor xenografts of either MDA-MB-231 or MDA-MB-468 significantly inhibited tumor growth and resulted in 87% and 80% tumor growth inhibition, respectively, without apparent host toxicity. Immunoblots of tumor tissue further demonstrate elevated levels of SYVN1 and decreased Mnk1/2 and p-eIF4E, which further confirms the role of SYVN1-mediated proteasomal degradation of Mnk1/2 in inhibiting TNBC tumor growth by VNLG-152R. Conclusion: As VNLG-152R potently inhibits development and progression of TNBC of different origins by upregulating E3 ubiquitin ligase SYVN1 leading to ubiquitination and proteasomal degradation of Mnk1/2 thereby decreased oncogenic phosphorylation of eIF4E by Mnk1/2, VNLG-152R could potentially be developed for the treatment of TNBC, irrespective of racial origin. Citation Format: Elizabeth Thomas, Retheesh S. Thankan, Puranik Purushottamachar, Vincent C. Njar. Mechanistic studies on VNLG-152R-mediated tumor inhibition of triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB235.